April, '12] 



HEADLEE: HESSIAN FI.Y 



105 



Of course, it is quite probable that this ratio ])etweeii normal 

 annual precipitation and the date of safe-sowing may not hold where 

 the precipitation reaches more than forty inches, but it is evident 

 that it must be taken into consideration when the rainfall is forty 

 inches or less. Hopkins' law of latitude and altitude must be modified 

 to include the operation of moisture as well as of temperature. 



Even after the entomologist has by means of experimental sowings 

 determined the normal date of safe-sowing in his territory, his work 

 is not done, for there have been and will be cases when for lack of 

 moisture or something else, the fly will be retarded, and, coming out 

 later, infest the wheat sown on the safe-sowing date just as seriously or 

 more seriously than sowings made either before or after. To avoid 

 this, the entomologist should adopt as the normal safe-sowing date 

 the average of dates on which the sowings of several years have been 

 found absolutely free from fly and should, when an outbreak is antici- 

 pated, keep a close watch on fly emergence. The date of safe-sowing 

 as shown in the following table follows within a day or two the maximu 

 emergence of the fly. 



Relation of Maximum Emergence to Date op Safe-sowing 



The field men can thus check up the progress of emergence and warn 

 the grower if the normal fly-free date is likelj" to prove too early or 

 materially later than necessary. 



President F. L. Washburn: Any discussion of this paper? 



F. M. Webster: The results of Doctor Headlee's investigations 

 are really not so surprising, but as a matter of fact, the exact influence 

 of humidity on Hessian fly has never before been so thoroughly inves- 

 tigated. There is a vast difference between the country east of the 

 Mississippi river and that west of it. There is a difference between 

 the humidity of eastern Kansas and that of western Kansas, so that 

 Doctor Headlee has a grand opportunity to study this problem. I 

 do not know of any state in the union that offers the same conditions. 



While the data he has given from Ohio is not that for which I am 

 responsible, nevertheless I think that he has done a most excellent and 

 creditable piece of work, and I see no reason whatever for criticizing 

 the accuracy of the results as given. As a matter of fact, we have a 



